The present invention relates to a rod lens to be fitted in endoscopes.
Endoscopes of this type have been marketed by Karl Storz GmbH & Co. KG, Tuttlingen, for several decades.
Endoscopes are generally used in minimally invasive surgery for observing body cavities and hollow organs.
Endoscopes have an oblong endoscope shaft in which components of an optical system are arranged. Further devices, usually a light-supply device and conduits for instruments, irrigation liquid for the like, are, moreover, provided inside the shaft. The light is usually supplied via light-guiding glass fibres.
The applicant developed and produced its first endoscope with a traditional lens system in 1953.
The invention of the “Hopkins rod-lens system” (catalogue of Karl Storz GmbH & Co. KG, Tuttlingen, “STORZ, DIE WELT DER ENDOSKOPIE, TECHNISCHE ENDOSKOPIE”, 9th edition Jan. 2002), which was developed by Karl Storz in cooperation with Professor H. H. Hopkins, was the most crucial breakthrough since the development of the conventional lens system by Nitze in the year 1879.
In Hopkins rod-lens systems, long rod lenses made of glass are used instead of the conventional lenses. These rod lenses have the advantage that they can be used to guide light in an endoscope, for example, with a significantly higher efficiency than is possible using conventional lenses, between which lies a relatively large air space.
The Hopkins rod-lens system thus meets the highest demands of medical diagnostics on account of its excellent image brightness, realistic display and light transfer which is significantly higher compared to the traditional lens system.
At the same time it became possible to crucially reduce the diameter of the endoscope. It was this development, in particular, through which the endoscopes with the Hopkins rod-lens system found wide-spread application in gentle minimally invasive surgery.
The optical system of rigid endoscopes is usually received in a pipe inside the endoscope shaft. Endoscope shafts are very long with respect to their diameter, and conventional diameters are usually in the region of a few millimetres, the length in the region of several decimetres. Accordingly, the diameter of a rod lens is very small with respect to its length, which is several centimetres.
Subjecting the shafts of the endoscopes to bending is inevitable when handling medical endoscopes. Bending of the thin and long endoscope shafts can lead to the relatively long rod lenses made of glass material chipping or even breaking. Damage of this type renders an optical system useless and usually the entire optical system needs to be replaced.
DE 31 13 110 C2 describes giving the rod lenses the shape of a bone in order to produce contact points only at the ends and thereby reduce the risk of breakage.
A further attempt is described in U.S. Pat. No. 4,148,551.
A plurality of rod lenses, which are arranged in the pipe located in the endoscope shaft, are connected to one another by way of a flexible tube. The flexible tube connects two neighbouring rod lenses.
The possibility of bending the endoscope shaft within certain limits without breaking the rod lenses in the process, however, is only partly achieved because of the flexible connection of the rod lenses by using the tube.
If bending moments act directly on the individual rod lens, the rod lens can still break. Such bending moments which act at a point can occur if an endoscope shaft hits an edge, or is dropped, during handling.
It is an object of the invention is to provide a rod lens of the type mentioned in the introduction which can absorb bending moments, in particular bending moments acting at a point, which occur during the use of an endoscope, without the risk of breaking the rod lens.